Wound healing is a process critical to the survival of the species after injury. Twenty years ago, it was shown that eosinophils are components of the inflammatory infiltrate in rat incisional cutaneous wounds (Bassett et al., 1977, Br. J. Exp. Pathol., 58: 581-605); however the importance of the presence of eosinophils remains unclear. Eosinophils have been implicated in the regulation of collagen metabolism (Hibbs et al., 1982, Biochem. J., 207: 621-624) and have been shown to elaborate transforming growth factor-alpha (TGF-.alpha.) (Elovic et al., 1990, Am. J. Pathol., 137: 1425-1434; Wong et al., 1990, J. Exp. Med., 172: 673-81) and transforming growth factor-beta 1 (TGF-.beta.1; Wong et al., Blood, 1991, 78: 2702-2707), two multifunctional cytokines of importance in wound healing (Schreiber et al., 1986, Science, 232: 1250-1253; Pierce et al., 1989, J. Cell Biol., 109: 429-440; Quaglino et al., 1990, Lab. Invest., 63: 307-319). In a hamster model, eosinophils have been demonstrated to infiltrate prominently into open skin wounds, where they represent a cellular source of TGF-.alpha. and TGF-.beta.1 at both mRNA and protein levels (Wong et al., 1993, Am. J. Path., 143: 130-142), and the expression of TGF-.beta.1 and TGF-.alpha. by eosinophils in oral wounds has been characterized in some detail (Yang et al, 1996, Am. J. Physiol., 270: G191-G202).
Eosinophils are a distinct lineage of granulocytes which originate from the bone marrow, circulate in the blood and emigrate into peripheral tissues (Spry, 1988, Eosinophils, ed. C. Spry, Oxford University Press, New York). Although eosinophils normally comprise only .about.3% of circulating leukocytes in humans, large numbers of mature eosinophils are especially abundant near the mucosal surfaces of gastrointestinal, respiratory, and genitourinary tracts (Spry and Tai, 1976, Clin. Exp. Immunol., 24: 423-434). In addition, greatly increased numbers of eosinophils appear in the blood and tissues associated with immune responses or disease processes such as helminthic parasitic infections, allergic diseases, and other pathological states with less well-defined causes (Weller, 1991, N. Engl. J. Med., 324: 1110-1118).